Electrochromism is a phenomenon that is known since the XIXth century by indirect observation. In 1815 Berzelius observed that tungsten oxide showed chromatic variations when subjected to a reductive (redox) environment. Since then several authors have devoted themselves to the study of this phenomenon, until a first patent application regarding an electrochromic device has been filed in 1929.
Systems based in electrochromic materials display changes of color, color density or opacity rate in response to an electric current or field. The active agent, an electrochromic material, is responsible for the variation in color according to its oxidation state controlled by the potential difference which is imposed between two electrodes, in the case of the electrochromic redox process. Different electrochromic materials have been studied, academically and commercially, a diversity of compounds exist which range from simple organic and inorganic molecules to transition metal compounds and polymers, e.g., U.S. Pat. No. 3,819,252 dated Jun. 25, 1974.
The state of the art currently comprises applications in the field of visualization. Electrophoresis is a recent technology used by companies such as E-INK (www.eink.com). The present invention does not relate to electrophoresis.
Specifically, there is a development in the field of electrochromic visualization devices, for example the “wafer thin” color displays developed by Siemens.
Touchscreens date back to 1970, as seen in U.S. Pat. Nos. 3,662,105 and 3,798,370.
Current touchscreens are made of two different devices, working together: the visualization device, and the device which detects a touch via one of several technologies:                detection of electric capacity variation in a capacitive film placed on the screen;        activation of electric contacts at the touch point; or        optical or sound triangulation.        
There remains a need for a combined device that performs the combined function of visualization and touch detection.
The implementation of the visualization and touch detection functions into a single electronic structure is the basis of the present invention.